Angled rotary tissue cutting instruments have become widely accepted for use in various surgical procedures to cut anatomical tissue at a surgical site within a patient's body. Angled rotary tissue cutting instruments typically comprise an elongate angled outer member and an elongate flexible inner member rotatably disposed within the angled outer member. A cutting element at a distal end of the inner member is exposed from an opening at a distal end of the outer member to cut anatomical tissue at the surgical site when the inner member is rotated within the outer member. The inner member is ordinarily rotated within the outer member via a powered surgical handpiece coupled to proximal ends of the outer and inner members, with the handpiece being maintained external of the patient's body. The outer member has one or more angled, curved or bent regions along its length to provide an angled configuration that facilitate positioning of the cutting element at the surgical site when the instrument is introduced in the patient's body, and particularly when the instrument is introduced through a narrow or small size, natural or artificially created entry opening in the patient's body. The inner member is provided with one or more flexible regions to reside within the one or more angled, curved or bent regions of the outer member for transmitting torque to rotate the cutting element while conforming to the angled configuration of the outer member. The angled configuration of the outer member is particularly beneficial in facilitating positioning of the cutting element at the surgical site where there is a non-linear path in the body form the entry opening to the surgical site. In such cases, angled rotary tissue cutting instruments are usually better suited to access the surgical site more easily and quickly, and with less trauma to the patient, than are rotary tissue cutting instruments in which the outer member is longitudinally straight.
In many surgical procedures performed using rotary tissue cutting instruments, the internal lumen of the inner member is used to transmit suction to the surgical site to aspirate anatomical tissue and/or fluid through the inner member. In addition, an annular gap or clearance between the internal diameter of the outer member and the external diameter of the inner member is commonly used as an irrigation passage to supply irrigation fluid to the surgical site. While rotary tissue cutting instruments with curved or bendable shafts have been used for some time, these shafts typically employ a single spirally wound strip of material to impart flexibility while transmitting torque. Unfortunately, spirally wound shafts and couplings tend to unwind when rotated in a direction opposite their winding so that torque can only be transmitted efficiently in one direction. A loss of irrigation can occur due to the inner member including spiral cuts or coils along the flexible region formed gaps as the inner member rotatably conforms to the angled configuration of the outer member while rotating. The loss of irrigation can be critical in many applications. For example, in a neuro tumor resection device, Micro-Electro-Mechanical (MEM) component are often used in which the loss of irrigation can cause the device to clog, leading to failure. In other devices, such as in an Ear-Nose-Throat (ENT) micro-debrider, the device can become less effective with the loss of irrigation due to not having enough saline at the cutting tip.
Angled rotary tissue cutting instruments continue to be extremely useful. There is a need for an elongated tubular assembly capable of maintaining sufficient strength and rigidity when transmitting torque via the flexible regions, and prevent a loss of irrigation, particularly considering that angled rotary tissue cutting instruments must oftentimes be designed to operate at high rotational speed and to withstand the forces imposed when cutting hard or tenacious anatomical tissue.